This disclosure relates generally to mixers for mixing fluids, and more particularly, to mixer impellers for such mixing devices.
Mixer impellers are used to mix, blend and agitate fluids and fluids with suspended solids in tanks or other vessels. Mixer impellers typically are mounted on a shaft driven by a motor that may be located outside the tank or vessel.
A mixer impeller may include a hub, adapted to be mounted on the shaft, and a plurality of blades extending radially outwardly from the hub in a plane perpendicular to the axis of rotation of the shaft and hub. The blades may be formed integrally with the hub, or alternatively, the blades may be bolted to flanges formed on the hub.
In a typical configuration, a mixer impeller is mounted on a shaft oriented vertically and centrally within a cylindrical tank so that the mixer impeller is concentric with the circular inner walls of the tank. Alternatively, a mixer impeller may be mounted on a shaft that extends sidewardly through a wall of a tank or vessel.
It is often desirable to design a mixer impeller such that the blades thereof maximize pumping efficiency, which is the ratio of the axial thrust developed by the impeller blades to the horsepower required to rotate the shaft. Accordingly, radial and rotational fluid flow resulting from operation of the impeller should be minimized. By increasing the efficiency of a mixer impeller, the horsepower required to achieve a given mixing rate may be reduced, thereby saving energy and equipment costs necessary to achieve a given performance level.
In addition, a higher efficiency impeller can achieve the same mixing effect with a smaller blade length, thereby reducing equipment costs. It is also desirable to design a mixer impeller wherein the mixing efficiency varies minimally relative to changes in the ratio of the impeller diameter to tank diameter, for applications in which the impeller is mounted concentrically within a cylindrical mixing tank.